In this post, I focus on writing a Groovy script that takes an existing Ant build file (often called build.xml) as input and generates a Groovy script that executes the same tasks defined in the build file. A few things about Groovy make this generation of code easier and I mention them as relevant in the post.

If one only wanted to execute the targets of the Ant file, I probably would just use Ant. If I wanted to run the targets as-is from an existing Ant file, I would probably use the approach I discussed in Executing Ant Build File Targets from Groovy. However, if I would like my Groovy code to execute some new targets in addition to or adapted from existing Ant build files, a good starting point would be a script like that I cover in this post. The code in this post could be extended to convert an existing Ant build file into Groovy code that could then be altered and enhanced as desired. This might be easier than trying to write the Groovy build code from scratch.

The source Ant build file used for the example in this post is called build.xml and is contained in the next code listing. It's a simple build file with some basic targets, but it is enough to demonstrate the concept of generating a Groovy script that performs the same as an Ant build file. Note that what the application this Ant file builds is not so important for what is covered here, but its related blog post is Effective Java NullPointerException Handling.

The Ant build file is specified in XML. The good news here is that Groovy makes XML parsing very easy with either XmlSlurper or XmlParser (I use the former in this post). Indeed, one can easily parse this entire XML file with Groovy with very little challenge. However, the use of Ant's ProjectHelper and Project classes in conjunction with Groovy's XML parsing make the script generation a little cleaner because those two Ant classes do some of the heavy lifting for us in terms of providing project basics (name, description, default and other targets).

The above generated script can then be run to execute the same targets as in the original Ant build file. The next series of screen snapshots indicate running the generated Groovy script. The first image shows the "default" case where no target name is specified and the functionality is equivalent to that when the Ant build file's default is used. The other images demonstrate passing various target names to the generated script. Although the generated code is a little verbose in handling these options, it's not a big deal because it is generated code.

As the above images indicate, the generated Groovy script can now be used to execute targets in a manner very similar to running them via Ant directly.

It is the use of AntBuilder that makes the generated script relatively short and easy to generate. A second purpose of this post after demonstrating generation of a Groovy build script from a source Ant build file is to also demonstrate AntBuilder used for various tasks such as making directories, cleaning, compiling, archiving, and generating Javadoc. The last shown Groovy code listing (the generated Groovy script) is contains several examples of AntBuilder in action.

I am confident that the original script could be made even leaner, but it does its job for the simple example build.xml file. The script only covers tasks and task attributes that exist in this particular source XML file, but could be easily extended to cover more Ant tasks and more attributes for the already covered Ant tasks.

Conclusion

Groovy is useful for all types of tasks related to development. In this post, I've shown how Groovy can be used to generate more Groovy code that mimics what an input Ant build file does. From this point, one could modify and enhance the generated script to suit particular script-related needs.